The present invention relates to threaded inserts for connecting fastening devices to workpieces and, more particularly, to a threaded insert for connecting studs and bolts to relatively soft or lightweight materials.
Studs and bolts are commonly installed in workpieces and the like for use in connecting panels, equipment and various other components to the workpiece. When the workpiece is made of steel or similar high strength materials, the workpiece usually is prepared to receive the bolt by drilling a hole in the workpiece and then tapping the hole to provide female threads to receive the male threads of the bolt. In most instances, the female threads formed in the workpiece are strong enough, due to the hardness of the steel material, to retain the bolt without stripping or otherwise damaging the workpiece. However, when the bolt must be installed in a workpiece made of a relatively soft or lightweight material, such as aluminum castings or composite materials, then the hole in the workpiece designed to receive the bolt must be specially prepared.
When using relatively soft or lightweight materials, the workpiece hole is drilled and tapped, similar to the drill and tap procedure used with workpieces made of steel materials. If the workpiece hole is tapped in the usual manner with threads that match the bolt threads, however, then a straight connection between the bolt and workpiece is weak and prone to failure, because the soft nature of the workpiece material and resulting threads usually are not strong enough to hold the bolt under typical operating loads. Hence, the workpiece threads are susceptible to stripping, resulting in a failed connection and oftentimes damage to the workpiece.
To solve the foregoing problems, it is common to use a threaded insert installed in the workpiece hole to receive the bolt. These inserts usually comprise a multi-piece insert assembly having an inner and outer thread with a retaining device. The outer insert has external threads for connection to the threaded hole in the workpiece. It also has internal threads for connection to external threads on the mating bolt or stud. The external threads on the outer insert usually are larger than the bolt threads to provide a more secure connection to the workpiece. In addition, the threaded insert frequently is swaged into the workpiece hole to create an even more secure connection, or a lock ring is used with tangs or serrations designed to broach into the workpiece to prevent rotation of the insert assembly.
During installation of multi-piece insert assemblies of the type described above, problems have been encountered in several areas. For example, some insert assemblies require multiple steps in which the insert is first threaded to the workpiece hole in one step and then the locking device is subsequently pressed or struck to retain the insert in another step. These multiple swaging operations can be time consuming and increase labor costs. Another area of concern involves damage to the workpiece during installation of the insert assemblies. When broaching is involved, oftentimes a striking or other force is applied to broach the material to attach the insert to the material of the workpiece. These forces can cause damage to the workpiece requiring replacement and increased costs. These forces also can remove protective coatings or finishes on the workpieces and allow corrosion to occult.
Accordingly, there has existed a need for an insert assembly that can securely attach a bolt or stud to a workpiece made from a soft or lightweight material, which is relatively simple and quick to install, and which does not cause damage or other harmful effects to the workpiece during the installation process. The present invention satisfies these needs and provides further related advantages.